. It arose from a dispute between Queen Elisabeth I and the Earl of Northumberland over the expropriation of copper ore mines containing gold. The court invoked the de minimis maxim stating that any action for waste (i.e. for depleting the value of an estate) against the beneficiary of an inherited estate would fail if the reduction in the value of the estate caused by the waste was minimal
. From its first use in the courtroom, de minimis was a blunt tool used by the court to reply “not in my court” to an unworthy claim. The main rationale appears to have been to avoid wasting the court’s time with minor claims.
The maxim’s prominence in complex multiple exposure disease claims rests on its original use in the much-cited case of Bonnington Castings v Wardlaw. In Bonnington, the House of Lords held that where an injury had two causes, one tortious and the other innocent, the pursuer only had to show that the contribution of the tortious exposure was more than de minimis to succeed in relation to causation. In this context, de minimis was said to be the converse of material and therefore causation was proved by way of material contribution to the injury. Pandora’s box was opened, paving the way for equating the non-exclusion of an issue from proceedings to the positive proof of causation if a contribution was more than extremely minimal. No definition of de minimis was analysed in Bonnington because the contribution to injury in that case was clearly material and at least causative to some extent.
Bonnington should now be understood as a case involving a divisible injury, namely pneumoconiosis, where the respective dust exposures caused identifiable proportions of the claimant’s injury. If the same issue had been litigated today, then the Defendant would have been liable to the extent of the injury that the tortious dust exposure had caused, on an apportionment basis. However, Bonnington has been much cited in cases concerning indivisible injuries, such that it is seen as part of the trail of authority through McGhee v The Coal Board resulting in the Fairchild exception. Recent attempts have been made in the Privy Council in Williams and in the Court of Appeal in Heneghan to rely upon Bonnington in the context of a claim for an indivisible injury, wrongly arguing for the application of material contribution to damage approach. It is difficult to see this area of law as being other than confusing given the lack of clarity in the application of the term ‘material contribution to damage’, and the largely unanalyzed use of the term de minimis.
Accepting that Bonnington was a case of divisible injury, then if the issue of the extent of contribution had been raised, then it would be reasonable to accept that the Claimant would have to prove a divisible portion of his injury to the same standard as a Claimant would have to prove any injury at all (i.e. on the balance of probabilities), in particular following the decision of the House of Lords in Rothwell. In Rothwell, the House of Lords was concerned with the question of whether pleural plaques amounted to a material injury. This was analysed in terms of whether the Claimant was “materially worse off” in functional and practical terms as a result of the relevant injury. Insofar as the expression “de minimis” was used in Rothwell, it was treated as the converse of “materially worse off”. In a claim for pneumoconiosis such as Bonnington, if pursued at the present date, it might reasonably be argued that the Claimant would have to show that the contribution from tortious exposure was such as to make him materially worse off in practical and functional terms. If the Claimant was able to show he was ‘materially worse off’, as result of the tortious exposure, the Claimant would have proved that the Defendant had caused him to suffer a material injury. This result would be achieved without any resort to the concept of de minimis.
Nonetheless, a tendency has persisted to use the term “de minimis” not as the converse of a contribution to injury that is material in a practical and functional sense. Rather, the term is used in an impressionistic and subjective way to connote something that is so slight as to be scarcely discernible. If it was found that the Claimant was ‘materially worse off’, then the de minimis threshold would always be passed. However, it does not necessarily follow that every contribution which is more than de minimis would make the Claimant materially worse off. In this way, the inquiry has been flipped on its head and the de minimis maxim used as a positive indicator of causation. This tendency has been brought into focus by decisions in the past year and this issue is likely to undergo further scrutiny in the appellate courts.
In Carder v Secretary of State for Health (1), University of Exeter (2)  EWHC 2399 (QB), a Defendant who was only liable according to agreed evidence for 2.3% of a Claimant’s asbestos exposure resulting in asbestosis argued that this did not amount to a material injury. At the trial before His Honour Judge Gore QC, Dr Rudd gave evidence on behalf of the Claimant. In answer to written questions prior to trial, he was asked as to his view of “de minimis” or “material” in this context. He indicated a view that he had previously expressed, that contributions of less than 1% to total dose could be considered to be de minimis. He indicated that this was from a “common sense” point of view, but on this basis a contribution of 2.3% was material, though very small.
Subsequently, in answer to questions from the Defendants, Dr Rudd confirmed in a series of answers that the Claimant’s actual function and symptomology would not have been either “notably different” or “materially different” or “measurably or demonstrably different”.
On this basis, the Defendants argued that absent the 2.3% exposure for which they were responsible, the Claimant’s position would have been, in practical terms, identical and therefore there was no material injury.
However, his Honour Judge Gore, QC, rejected this argument, giving a number of reasons for so doing, but the first and probably most important was in paragraph 33 of the judgment,
“First, 2.3% though very small was, in the opinion of Dr Rudd from a medical perspective, material and beyond de minimis”.
It should be noted that Dr Rudd was using the terms ‘material’ and ‘not de minimis’ synonymously and that his approach to assessing what was de minimis which he described as ‘common sense’, would have to be considered impressionistic rather than scientific. The judicial reasoning therefore adopting this appears to accept a definition of ‘material’ falling short of the approach in Rothwell, that is that the Claimant must be ‘materially worse off’. This illustrates the problem of using an exclusionary tool in a positive way to prove causation. Such an approach might have been justified in the 16th Century when judges were not assisted by expert evidence and had to be guided by their own instincts and impressions. It is difficult to see how a judge can reach a view that the contribution was in effect ‘material’ when an authoritative expert such as Dr Rudd had indicated it was not.
In Heneghan, the issue arose as to what was the correct approach to legal causation in cases involving carcinoma of the lung, allegedly caused by asbestos exposure. Mr Justice Jay was upheld by the Court of Appeal in finding that the correct approach was that based on the Fairchild exception and that accordingly damages should be apportioned following the decision in Barker v Corus. We have already indicated in the article “Heneghan. Heads I win, tails you lose?” that the decision is problematical in apparently permitting both conventional causation and the Fairchild exception to be applied to cases involving asbestos related carcinoma of the lung, depending on the extent of proof by the Claimant.
However, for present purposes, another difficulty arises, as reflected in the evidence of Dr Rudd again; that it is likely the Deceased in Heneghan would have contracted carcinoma of the lung as a result of his global asbestos exposure, even in the absence of the lowest exposure alleged against a Defendant, that is one of 2.5%. Notwithstanding this evidence, damages were awarded on an apportioned basis against this lowest-exposure Defendant. However, it could reasonably be questioned whether this exposure should be considered material if it was accepted that the Deceased would have suffered from carcinoma of the lung as a result of asbestos exposure in the absence of this slight, additional exposure. It is difficult to see how something can be said to mean material in terms of contribution, either to damage or risk, if the evidence establishes that the relevant damage or risk would have occurred in any event.
Most recently in Mayne v Atlas Stone Company (1), Wheatley Winton Hayes Limited (2), Walker Bros (Darlington) Limited (3) , EWHC 1030 (QB), the Defendants failed in a similar argument to that deployed in the Carder case. In Mayne, the Deceased was found to have suffered a 5% disability in his lifetime, resulting from pleural thickening. This was in the context of an overall disability of 70% to 80%. In other words, the deceased’s disability arose substantially from other causes. The Second Defendant, who took issue as to whether they were a cause of any injury, had contributed 8.16% of the Deceased’s asbestos exposure. The contribution was therefore a very small proportion, 8.61%, of a very small, 5% disability. Mathematically, the Defendant caused a 0.62% disability. Unsurprisingly, questions asked of the medical experts had confirmed that the exposure for which the Defendant was responsible had made no practical or functional difference to the Deceased. On this basis, the Defendant sought to argue that the Deceased had not been materially worse off as a result of the relevant exposure and therefore there was no actionable damage caused by them. The Judge, Mrs Justice Cox, rejected this argument. Her basic reasoning for so doing appears to reflect policy rather than legal principle, in paragraph 32 of the judgment, the judge stated:
“The suggestion that a Claimant seeking damages for asbestos-related disease must go on to prove in addition that a particular Defendant made a material contribution to his disease process, in the sense that the contribution of itself gave rise to a discernible or measurable injury is unwarranted and is in my view unsupported by authority. Such a requirement would ignore the totality of the Claimant’s exposure to asbestos during his working life and the quantifiable disability caused by the exposure. It would not accord with either the reality of this industrial disease or, as Stuart Smith LJ saw it, “common sense”. It would lead, in my view, to uncertainty and to arbitrary results and unfairness, both to Claimants and among Defendants.”
With respect to the Judge, this line of reasoning is hard to understand. Requiring a Claimant to prove that a Defendant has in fact injured the Claimant in a material way would not ordinarily be considered arbitrary or unfair. That a claim might fail in causation where breach of duty is proved is implicit in the requirement of causation as a separate part of proof of injury. This illustrates again the use of ‘non de minimis’ as indicating positive proof of causation when the injury is in fact shown to be less than material.
It appears likely, therefore, that the courts will have to address in the near future at appellate level the question of whether the concept of de minimis should be used in this context and if so how it is to be applied. It will be argued that following Rothwell, the threshold of proof of causation of a discernible apportion of injury should be applied in the same way as proof of injury in itself. If this approach was taken, it would be difficult to see in what way the relevance or value of the historic concept of de minimis would assist. Perhaps the time has come to return it to the Elizabethan copper mines.
 The Queen v The Earl of Northumberland (1567) 75 E.R. 472
 Ibid at 
 Bonnington Castings v Wardlaw  A.C. 613
 Ibid, at p.621
 McGhee v National Coal Board  1 W.L.R. 1
 Fairchild v Glenhaven Funeral Services Ltd  1 A.C. 32
 Williams v Bermuda Hospitals Board  UKPC 4
 Heneghan v Manchester Dry Docks  EWCA Civ 86
 Rothwell v Chemical and Insulating Company Limited and others  UKHL 39
Supra fn 8, at 
 Barker v Corus  UKHL 20